A flat-panel CRT display basically consists of an electron-emitting device and a light-emitting device. The electron-emitting device, commonly referred to as a cathode, contains electron-emissive elements that emit electrons over a wide area. The emitted electrons are directed towards light-emissive elements distributed over a corresponding area in the light-emitting device. Upon being struck by the electrons, the light-emissive elements emit light that produces an image on the viewing surface of the display.
The electron-emitting and light-emitting devices in a flat-panel CRT display are connected together, typically through a largely annular outer wall, to form a sealed enclosure having an active region in which the electrons travel from the electron-emitting device to the light-emitting device. For the display to operate efficiently, the pressure in the sealed enclosure needs to be very low, typically a high vacuum of 10.sup.-6 torr or less. The exterior-to-interior pressure differential across the display is thus typically close to 1 atm.
The electron-emitting and light-emitting devices of a flat-panel CRT display are usually quite thin. In a flat-panel CRT display of significant viewing area, e.g., at least 10 cm.sup.2, the electron-emitting and light-emitting devices are normally incapable of resisting the exterior-to-interior pressure differential on their own. Accordingly, a spacer (or support) system is typically provided inside the sealed enclosure to prevent air pressure and other external forces from collapsing the display. The internal spacer system also maintains a relatively uniform spacing between the electron-emitting and light-emitting devices.
The spacer system typically consists of a group of laterally separated spacers positioned so as to not be visible on the display's viewing surface. The spacers can be shaped in various ways such as walls or posts. Regardless of how the spacers are shaped, electron flow through the display occurs in portions of the active region not occupied by the spacers.
The presence of the spacer system can adversely affect the electron flow. For example, electrons can occasionally strike the spacer system, causing it to become electrically charged. The potential field in the vicinity of the spacer system changes. Consequentially, the electron trajectories are affected, often leading to degradation in the image produced on the viewing surface. As discussed in Spindt et al, U.S. Pat. No. 5,532,548, and Schmid et al, U.S. Pat. No. 5,675,212, electrodes are typically provided along the faces of the walls of a spacer system to overcome certain adverse affects that arise from the presence of the spacer walls.
In short, spacer system design is a critical part of overall flat-panel CRT display design. The spacer system is subjected to a variety of environmental conditions. It is important that the spacer system be capable of accommodating a wide range of environmental conditions without causing image degradation.